Chapter 4. Configuring custom certificate authorities

1. Copy the certificates and keys to the preferred directory in the host operating system. Ensure that the files are accessible by root only.

2. Update the MicroShift configuration for each custom CA by specifying the certificate names and new fully qualified domain name (FQDN) in the MicroShift /etc/microshift/config.yaml configuration file.

   Each certificate configuration can contain the following values:

   • The certificate file location is a required value.

   • A single common name containing the API server DNS and IP address or IP address range.

     Tip

     In most cases, MicroShift generates a new kubeconfig for your custom CA that includes the IP address or range that you specify. The exception is when wildcards are specified for the IP address. In this case, MicroShift generates a kubeconfig with the public IP address of the server. To use wildcards, you must update the kubeconfig file with your specific details.

   • Multiple Subject Alternative Names (SANs) containing the API server DNS and IP addresses or a wildcard certificate.
   • You can provide additional DNS names for each certificate.
3. After the MicroShift service restarts, you must copy the generated kubeconfig files to the client.
4. Configure additional CAs on the client system. For example, you can update CA bundles in the Red Hat Enterprise Linux (RHEL) truststore.
5. The certificates and keys are read from the specified file location on the host. Testing and validation of configuration is done from the client.
6. External server certificates are not automatically renewed. You must manually rotate your external certificates.

Procedure

1. Copy the custom certificates you want to add to the trust root of the MicroShift host. Ensure that the certificate and private keys are only accessible to MicroShift.

2. For each custom CA that you need, add an apiServer section called namedCertificates to the /etc/microshift/config.yaml MicroShift configuration file by using the following example:

   apiServer:
     namedCertificates:
      - certPath: ~/certs/api_fqdn_1.crt 1
        keyPath:  ~/certs/api_fqdn_1.key 2
      - certPath: ~/certs/api_fqdn_2.crt
        keyPath:  ~/certs/api_fqdn_2.key
        names: 3
        - api_fqdn_1
        - *.apps.external.com

   1

   Add the full path to the certificate.

   2

   Add the full path to the certificate key.

   3

   Optional. Add a list of explicit DNS names. Leading wildcards are allowed. If no names are provided, the implicit names are extracted from the certificates.

3. Restart the {microshift-service} to apply the certificates by running the following command:

   $ systemctl microshift restart

4. Wait a few minutes for the system to restart and apply the custom server. New kubeconfig files are generated in the /var/lib/microshift/resources/kubeadmin/ directory.
5. Copy the kubeconfig files to the client. If you specified wildcards for the IP address, update the kubeconfig to remove the public IP address of the server and replace that IP address with the specific wildcard range you want to use.

6. From the client, use the following steps:

   1. Specify the kubeconfig to use by running the following command:

      $ export KUBECONFIG=~/custom-kubeconfigs/kubeconfig 1

      1

      Use the location of the copied kubeconfig file as the path.

   2. Check that the certificates are applied by using the following command:

      $ oc --certificate-authority ~/certs/ca.ca get node

      Example output

      oc get node
      NAME                             STATUS   ROLES                         AGE   VERSION
      dhcp-1-235-195.arm.example.com   Ready    control-plane,master,worker   76m   v1.30.3

   3. Add the new CA file to the $KUBECONFIG environment variable by running the following command:

      $ oc config set clusters.microshift.certificate-authority /tmp/certificate-authority-data-new.crt

   4. Verify that the new kubeconfig file contains the new CA by running the following command:

      $ oc config view --flatten

      Example externally generated kubeconfig file

      apiVersion: v1
      clusters:
      - cluster:
          certificate-authority: /tmp/certificate-authority-data-new.crt 1
          server: https://api.ci-ln-k0gim2b-76ef8.aws-2.ci.openshift.org:6443
        name: ci-ln-k0gim2b-76ef8
      contexts:
      - context:
          cluster: ci-ln-k0gim2b-76ef8
          user:
        name:
      current-context:
      kind: Config
      preferences: {}

      1

      The certificate-authority-data section is not present in externally generated kubeconfig files. It is added with the oc config set command used previously.

   5. Verify the subject and issuer of your customized API server certificate authority by running the following command:

      $ curl --cacert /tmp/caCert.pem https://${fqdn_name}:6443/healthz -v

      Example output

      Server certificate:
        subject: CN=kas-test-cert_server
        start date: Mar 12 11:39:46 2024 GMT
        expire date: Mar 12 11:39:46 2025 GMT
        subjectAltName: host "dhcp-1-235-3.arm.eng.rdu2.redhat.com" matched cert's "dhcp-1-235-3.arm.eng.rdu2.redhat.com"
        issuer: CN=kas-test-cert_ca
        SSL certificate verify ok.

      Important

      Either replace the certificate-authority-data in the generated kubeconfig file with the new rootCA or add the certificate-authority-data to the trust root of the operating system. Do not use both methods.

   6. Configure additional CAs in the trust root of the operating system. For example, in the RHEL Client truststore on the client system. See The system-wide truststore for details.

      • Updating the certificate bundle with the configuration that contains the CA is recommended.
      • If you do not want to configure your certificate bundles, you can alternately use the oc login localhost:8443 --certificate-authority=/path/to/cert.crt command, but this method is not preferred.

Procedure

1. From MicroShift, ensure that the certificate is served by the kube-apiserver and verify that the certificate path is appended to the --tls-sni-cert-key FLAG by running the following command:

   $ journalctl -u microshift -b0 | grep tls-sni-cert-key

   Example output

   Jan 24 14:53:00 localhost.localdomain microshift[45313]: kube-apiserver I0124 14:53:00.649099   45313 flags.go:64] FLAG: --tls-sni-cert-key="[/home/eslutsky/dev/certs/server.crt,/home/eslutsky/dev/certs/server.key;/var/lib/microshift/certs/kube-apiserver-external-signer/kube-external-serving/server.crt,/var/lib/microshift/certs/kube-apiserver-external-signer/kube-external-serving/server.key;/var/lib/microshift/certs/kube-apiserver-localhost-signer/kube-apiserver-localhost-serving/server.crt,/var/lib/microshift/certs/kube-apiserver-localhost-signer/kube-apiserver-localhost-serving/server.key;/var/lib/microshift/certs/kube-apiserver-service-network-signer/kube-apiserver-service-network-serving/server.crt,/var/lib/microshift/certs/kube-apiserver-service-network-signer/kube-apiserver-service-network-serving/server.key

2. From the client, ensure that the kube-apiserver is serving the correct certificate by running the following command:

   $ openssl s_client -connect <SNI_ADDRESS>:6443 -showcerts | openssl x509 -text -noout -in - | grep -C 1 "Alternative\|CN"

Procedure

1. Stop the MicroShift services and clean up the custom certificates by running the following command:

   $ sudo microshift-cleanup-data --cert

   Example output

   Stopping MicroShift services
   Removing MicroShift certificates
   MicroShift service was stopped
   Cleanup succeeded

2. Restart the MicroShift services to recreate the custom certificates by running the following command:

   $ sudo systemctl start microshift